Marine System Analysis Group

Hydrogen sulfide, H₂S, is a chemical compound that is easily recognized by its smell of rotten eggs. The substance is toxic for most organisms and is formed in anoxic environments where sulphur is present. The Baltic Sea and the Byfjord is two examples of where hydrogen sulfide is common. In the Byfjord, hydrogen sulfide is present at relatively shallow depths, just beneath the sill level due to anoxic conditions. Every second to fifth year new saline and oxygen rich water manages to flow over the Sunningen sill and down into the deep water of the Byfjord, at least partly renewing some of the resident water. At these events, hydrogen sulfide is oxidized thus sharply reducing its concentration. However, the oxygen concentrations also decrease. When all of the oxygen is consumed, the build-up of hydrogen sulfide starts again. The BOX-project aims at mimicing this natural mechanism of water renewal in an artificial way, thus improving the oxygen conditions and remove the hydrogen sulfide permanently.

Phosphate accumulates in the deep-water during hypoxic conditions due to leakage from the sediments. During a renewal event, some of it is transported out of the deep-water, while some of it is thought to bound with the sediment. If phosphate finds it way out into the water column it could create a lot of problems. The largest problem is stimulating large algal blooms. This is a problem every summer in the Baltic Sea. If the sediments can be oxygenated, less phosphate will reach the surface water and algal blooms may be limited. This is one of the mechanisms that the BOX-project will try to figure out.

In the graph the total amount of hydrogen sulfide, oxygen and phosphate integrated over depth in the Byfjord is shown as metric tonnes. The figure is updated every time measurement is done in the Byfjord, typically once or twice per month.

Metric tonnes of hydrogen sulfide, oxygen and phosphate in the Byfjord (integrated between 20 and 40 metres depth). Note: Interpolating has been done, why these numbers should be taken only as indicative. Original data from the BOX-project and Bohuskustens Vattenvårdsförbund. The dashed line indicate pump start. Click on the image for a larger version.